Multilayer fibrous insulating article

ABSTRACT

A multilayer web or article of insulating material which essentially includes at least one flame-resistant layer having polyacyloxalamidrazone fibers bearing at least one metal, preferably zinc, tin or calcium, in chemically combined form. These articles or materials are especially suitable in the manufacture of rescue suits, protective clothing and protective linings.

lne lemae 55R 30 919- 132 1 3 (91'1" l l 1 United State y ,1 C 1 1 3,801,422 Giirlach et al. Apr. 2, 1974 MULTILAYER FIBROUS INSULATING ARTICLE [56] References Cited [75] Inventors: Helmut Gorlach; Walter Stroot, UNlTED STATES PATENTS both of Wuppertal-Elberfeld; Alois 3 573 261 3/19. Kersten et al 260 I78 TF Kmckl, Kelsterbach an of Germany 3,560,453 2/1971 SchiSpf et al. 260/78 TF [73] Assignee: Akzona Incorporated, Asheville,

NC. Primary Examiner-William A. Powell Assistant Examiner-James J. Bell [22] Filed: 1971 Attorney, Agent, or FirmJohnston, Keil, Thompson [21] Appl. No.: 119,847 & shul'tleff [30] Foreign Application Priority Data [57] ABSTRACT Mar, 6, 1970 Germany 2010598 A ultilay r web or article of insulating material which essentially includes at least one flame-resistant Cl layer having polyacyloxalamidrazone fibers bearing at 161/156, 161/213, 161/403, 260/73 least one metal, preferably zinc, tin or calcium, in It. chemically combined form These articles or materials Fleld sfial'ch 173, 175, are especially suitable in the manufacture of rescue suits, protective clothing and protective linings. 260/78 TF, 13; 117/118, 136, 137, 138.8 R; 264/184; 106/15 FP; 8/1155, 115.6, 115.7, 116 21 Clams, N0 Drawmgs sea-01422 A MULTILAYER FIBROUS INSULATING ARTICLE Rescue suits and protective clothing of the type used for example in aviation and navigation must satisfy very stringent requirements. They must generally provide protection against cold, fire and water. Various multipurpose materials for the manufacture of protective clothing or similar articles have become known. Most of these materials are both heat insulating and designed which keeps a body afloat and also a flame-proof heat insulating layer. The flameproof heat insulating layer in this instance consists of a carbonized textile sheet of cellulose threads and/or fibers. The use of carbonized material as flameproof layer, however, entails numerous disadvantages. The carbonized material has only a limited mechanical strength and is therefore difficult to fabricate and handle in producing an insulating article.

Moreover, it tends to disintegrate into a powder when subjected to mechanical stress, with the result that the flameproof layer is very quickly perforated or punctured and may finally partly or completely disintegrate. Sufficient protection against fire is then no longer ensured, and the protective garment or other article then becomes unusable.

In other known embodiments, the flameproof layer is made of some other diffieultly combustible or noncombustible material, for example fabrics of natural fibers which have been treated with a flame-resistant finish or coating are used, but these provide protection only at temperatures of up to about 250C.

Although metallized asbestos fabrics are often used as an outer layer to afford protection against radiant heat up to l,000C. and against flying sparks and brief contact with flames, they have the disadvantage of being heavy and having very little mechanical strength. These properties are unsatisfactory to fabricate or use as woven, knitted or otherwise coherent textiles. In addition, asbestos fabrics have a capillary action which makes them highly permeable to combustible liquid substances.

Metallized fabrics of glass fibers likewise afford pro-- tec'tion against radiant heat up to about 1,000C. but they are also heavy and in addition they are quite brittle. They tend to split or shatter into fragments and their use is therefore highly objectionable for reasons of health.

According to the present invention, it has now been found that a very substantial improvement can be achieved in a multilayer insulating material which is preferably used as an article for the manufacture of rescue suits, protective clothing or the like and which is usually formed by several layers of woven or knitted fabrics or fibrous fleeces. These layers may be quilted, stitched or bonded together and preferably include heat insulating, difficultly combustible and/or flameproof layers and also, if desired, layers which are capable of floating or of keeping an enclosed body afloat.

ln particular, it is an object of the invention to provide at least one flame-resistant layer in such insulating articles, whereby this layer will also exhibit desirable textile properties in its fabrication and subsequent use. Other objects and advantages of the invention will become more apparent in view of the following detailed specification.

The improvement of the present invention thus essentially involves a multilayer fibrous insulating article containing fibers composed of a polyacyloxalamidrazone in chemically combined form with at least one of the metals zinc, tin, cadmium, barium, stronium, calcium, antimony or tantulum. Especially good results have been achieved with the metal-containing polyacyloxalamidrazone when combined with a cellulosic polymer, the two polymers being spun in common from an aqueous alkaline solution and the metal subsequently introduced into the resulting filaments or fibers.

- For purposes of the present invention, the term flame-resistant" is employed with reference to a material which is relatively difficult to burn or substantially flameproof as well as preferably having some degree of heat insulating or other flame resistant properties. A multilayer fibrous insulating material is one which has at least two and preferably three or more fibrous layers, at least one of which must be flame-resistant for purposes of the invention. Such terms as fibers, filamerits, threads, yarns and the like are generally used interchangeably in this specification; for example fibers may include continuous filaments and woven materials as well as cut or staple fibers. All such fibers are characterized by their substantially linear molecular orientation adapting them to various textile uses.

Polyacyloxalamidrazones are known polymers which have recurring units of the formula:

R represents a straight chain or branched saturated or unsaturated aliphatic radical having two to 12 carbon atoms or a cycloaliphatie, araliphatic, aromatic or heterocyclic radical, preferably a substantially divalent hydrocarbon radical of two to six carbon atoms, i.e., a structure in which an occasional hetero atom such as oxygen, nitrogen or sulfur has no material effect. These polymers may be prepared according to conventional procedures, for example, by reacting oxalic acid bisamidrazone with one or more dicarboxylic acid dihalides by the process disclosed in Belgian Pat. No. 705,592. See also the procedure for preparing these polymers in US. Pat. No. 3,544,528.

The fibers of the desired metal compounds of polyacyloxalamidrazones may be produced, for example, by spinning a solution of apolyacyloxalamidrazone in a dilute aqueous alkali metal hydroxide into an acid precipitation bath and then reacting the resulting fibers with a solution of one or more soluble compounds of the metals selected from the group consisting of zinc, tin, cadmium, barium, strontium, calcium, antimony and tantalum.

The initial dissolution of the polyacyloxalamidrazone for spinning into filaments can follow the procedure, for example, as disclosed in copending application, Ser. No. 719,027, (now US. Pat. No. 3,583,953). Sodium and potassium hydroxide are preferably used as being most economical in the preparation of the dilute basic aqueous solution. In general, the polymer can feasibly be dissolved in such solutions up to as much as 30 percent by weight, but more usually about 4 to 20 percent and preferably 6 to l6 percent by weight. The acid precipitating bath does not differ substantially from those conventionally used in the production of viscose or similar cellulosic filaments. For example, one can use a relatively dilute aqueous solution of one or more organic or preferably inorganic acids, solutions of salts of strong acids with weak bases, or solutions of acid salts. The same spinning procedure is followed whether working with the polyacyloxalamidrazone alone or in combination with the cellulosic polymer.

Both the spinning of the filaments and the subsequent addition of the metal from its solution can be carried out at room temperature or at only moderately elevated temperatures. In general, the particular metals are best added to the polymer fiber or filament in their dissolved form as water-soluble salts or similar compounds in which the metal is present as an ion in aqueous solution. The amount of metal taken up by the polyacyloxalamidrazone fiber depends to some extent upon the particular polymer as well as the time of treatment. The exact form of chemical combination with the polyacyloxalamidrazone has not been determined, but since the metal is not easily washed from the fiber, it is apparent that there is a complex combination if not a direct ionic or valent bondage between the polymer and the metal. Thus, one may refer to a metallic polyacyloxalamidrazone or a chemical combination resulting in a polyacyloxalamidrazone-metal compound. With a sufficient amount of added metal, these polymers exhibit good to excellent flame-proofing or flameresistant properties.

Fibers of the polyacyloxalamidrazone-meta] compounds containing any desired proportion of cellulose may be produced by spinning a mixture of viscose and the aqueous alkaline solution of a polyacyloxalamidrazone into the acid precipitation bath and then reacting the resulting fibers or filaments with an aqueous solution of one or more compounds of the metals zinc, tin, cadmium, barium, strontium, calcium, antimony and tantalum. It is preferred, however, to form such bicomponent filaments or fibers using at least 20 percent and preferably 30 to 70 percent by weight of the polyacyloxalamidrazone.

Both the fibers of the above-noted metal compounds of polyacyloxalamidrazones and the fibers of cellulose with these metal compounds of polyacyloxalamidrazones have the advantage over known flame-resistant materials that, by virtue of their adequate textile strength and stretch properties, they can be easily worked up into woven and knitted fabrics and also into fibrous fleeces which retain their flameproof character even after repeated washing and cleaning. The comparative flexibility and textile handle of these metalcontaining polymers represents a very significant advantage.

The multilayer webs or sheets of insulating material as an article according to the invention may contain one or more flame-resistant layers of fibers of the aforesaid metal compounds of polyacyloxalamidrazones or fibers of these metal polymer compounds and cellulose. The more metal bound to the polyacyloxalamidrazone fibrous material, then the more flameresistant are the resulting layers. The structure of the web or layer of insulating material according to the invention, i.e., the sequence of the various layers of woven or knitted fabric and/or fibrous fleeces should be adapted to the particular purpose for which the article is intended in any given case.

Articles ofinsulating material according to the invention in which even the outermost layers must be flameproof preferably contain as at least one outer surface layer a woven or knitted fabric made of fibers which contain the polyacyloxalamidrazone-metal compounds. This is especially advisable when greater permeability to air is required.

Articles ofinsulating material according to the invention which are required to contain one or more flameproof layers in their interior advantageously contain as at least one inner layer of a relatively voluminous or bulky fibrous fleece which contains the polyacyloxalamidrazone combined with one or more of the specified metals.

The flame-resistant layers of the articles of insulating material according to the invention may be made of fibers which are uniform in character in that they consist of only one polyacyloxalamidrazone-metal compound but they may also contain mixtures of fibers which differ from each other in the polyacyloxalamidrazone and/or the bound metal. If the insulating material contains several such flame-resistant layers, the individual layers may be identical or different from each other in their composition of fibers. Those fibers which contain a polyacyloxalamidrazone-metal compound together with cellulose should contain at least 20 percent and preferably 30 to percent by weight of the polyacyloxalamidrazone and, correspondingly, up to percent and preferably 30 to 70 percent by weight of cellulose. Those fibers which consist of 40 to 50 percent by weight of polyacyloxalamidrazone and 60 to 50 percent by weight of cellulose have been found to be particularly suitable.

I 'According to a preferred embodiment, the articles of insulating material according to the invention have a weight of 300 to 1,000 grams per square meter (g/m and include at least one flame-resistant or difficultly combustible layer which contains 40 to percent of its weight in the form of a fibrous material of the aforementioned metal compounds of polyacyloxalamidrazones, the weight per square meter of these difficultly combustible layers being preferably 50 to 300 grams.

The metal content of the fibrous material is preferably at least 15 percent by weight based on'the polyacyloxalamidrazone content. Polyterephthaloyl oxalamidrazone-metal compounds have been found to be particularly suitable for use as a flame-resistant fibrous material, and among these particularly the compounds of zinc, tin and calcium. Other suitable organic dicarboxylic acids which provide the acyl" group of the polyacyloxalamidrazone include by way of example: adipic acid, sebasic acid, succinic acid, fumaric acid, glutaric acid, l,4-cyclohexane dicarboxylic acid, homoterephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, p,p'-diphenylether dicarboxylic acid and 2,6-pyridine dicarboxylic acid.

Although some flame-resisting properties are imparted by as little as 5-10 percent by weight of the metal with reference to the polyacyloxalamidrazone, the combination of at least 15 percent by weight of the metal with the polymer in the fibrous state generally ensures the minimum desired effect, depending upon the end use as well as the total content of metalpolymer fibrous material in a particular layer. When using substantial amounts of cellulosic polymer in the fibers together with the polyacyloxalamidrazone, it is often advantageous to increase the metal content to the maximum amount taken up by the fiber in an aqueous bath or solution of the soluble metal compound. The resulting fibers, filaments, yarns and the like as well as woven and knitted fabrics or non-woven webs and fleeces produced therefrom have the distinct advantage of exhibiting very good textile properties in addition to the required flame-resistance.

Insulating materials having a weight of up to 1,000 grams per square meter are especially suitable for use as protective clothing and rescue suits. Such insulating materials provide no difficulties in fabricating such clothes or suits and the articles made up from these materials provide the wearer with a high degree of protection against heat and flames as well as sufficient freedom of movement. in insulating materials used for this purpose, at least the fibrous outer surface layer which in the suit constitutes the layer furthest away from the body advantageously consists of a woven or knitted fabric of one or more of the aforementioned metal compounds of polyacyloxalamidrazones. If the flameresistant layer is used as the innermost layer, preferably in the form of a fibrous web or fleece, the surface layer may be in the form ofa woven or knitted fabric of poly- .amides (nylons), polyesters (e.g., polyethylene terephthalate) or mixtures of these polymers with cotton or with woven or knitted rayon fabrics which have been .treated with the usual commercial flame retarding agents.

Sheets or similar articles of insulating material which contain about to 50 percent of their total weight in the form of fibers of one or more of the aforesaid polyacyloxalamidrazonemetal compounds can be made up into rescue suits which have properties which are physiologically suitable for clothing. Thus, only about one-fifth to one-half of all of the total weight of all fibers in the multilayer insulating material is contributed by the particular metal-polymer fibers.

For a heat insulating layer it is particularly suitable to use a fleece of linear saturated fiber-forming polyester, for example crimped fleeces of polyethylene terephthalate fibers. The so-called floating layer or layer which can support a weight afloat may be made of the known high strength fabrics of continuous polyamide yarn which are coated with an elastomeric film to render them water-proof and resistant to sea water on one side.

A few practical examples of articles made with the multilayer insulating material according to the invention are given below merely by way of illustration. The sheets of insulating material are composed of several and at least two dissimilar layers. If the sheet is used for protective clothing or rescue suits, then the individual layers are so arranged that the first layer l as set forth in each example constitutes the layer which will be furthest away from the body and the last layer constitutes the layer closest to the body. The premeability to air was determined according to DIN 53 887 (German lndustrial Standards), using a Frank-Hauser test apparatus ata vacuum measured as a 20 mm. column of water. The thermal effect was determined by the method of A. Zart (E. Siebel, Handbuch der Werkstoffprufung,

2nd edition, Springer-Verlag, Berlin/Gottingen/Heidelberg, 1960, Volume 5, H. Sommer and F. Winkler, page l,l35).

The following examples illustrate but do not limit the invention to the specific features therein disclosed. All weights of the multilayer or composite articles in the form of sheets, webs or the like are given as weight per unit of covering area, i.e., grams per square meter or g/m in abbreviated form. The permeability of the multilayered article is measured in units of liters of air per cm. per minute, abbreviated as l/lOO cm -min. While the thermal efficiency is a measure of the flame-resistance, each individual layer consisting of or containing the polyacyloxalamidrazone-metal fibers was also tested and found to be flame-resistant in terms of being a difficultly combustible up to a substantially flame-proof layer.

EXAMPLE 1 l. Knitted polyamide fabric;-weight 132 g/m'.

2. Continuous fibrous fleece of a mixture of 40 percent of polyterephthaloyl oxalamidrazone and 60 percent of cellulose having a tin content of 30 percent by weight; weight 69 g/m 3. Crimped fleece of polyethylene terephthalate fibers; weight g/m 4. Continuous fibrous fleece of a mixture of 40 percent of polyterephthaloyl oxalamidrazone and 60 percent of cellulose having a tin content of 30 percent by weight; weight 69 g/m 5. Knitted rayon fabric dressed with 30 percent of tris-'(2,3-dibromopropyl) phosphate; weight 196 g/m.

The weight of this composite sheet of five layers'of insulating material is 616 g/mflthe permeability to air is 313 l/lOO cm min and the thermal efficiency is 61.4 percent.

EXAMPLE 2 l. Woven fabric of'a mixture of 67 percent of polyester and 33 percent of cotton; weight 200 g/m 2. Continuous fibrous fleece of a mixture of 40 percent of polyterephthaloyl oxalamidrazone and 60 percent of cellulose having a zinc content of 20 percent by weight; weight 69 g/m 3. Crimped fleece of polyester; weight 150 g/m 4. Fleece of a mixture of 40 percent of polyterephthaloyl oxalamidrazone and 60 percent of cellulose having a zinc content of 15 percent by weight; weight 69 glm 5. Knitted fabric ofa mixture of 40 percent of polyterephthaloyl oxalamidrazone and 60 percent of cellulose having a calcium content of 20 percent by weight; weight 286 g/m The weight of this multilayer sheet of insulating material is 774 g/m", the permeability to air is 103 l/lOO cm -min. and the thermal efficiency is 68.1 percent.

EXAMPLE 3 1. Knitted polyamide fabric; weight 132 g/m'.

2. Continuous fibrous fleece of a mixture of 40 percent of polyadipinoyl oxalamidrazone and 60 percent of cellulose having a zinc content of 15 percent by weight; weight 286 g/m.

3. Continuous fibrous fleece of a mixture of 40 percent of polyadipinoyl oxalamidrazone and 60 percm -min. and the thermal efficiency is 49.9 percent.

EXAMPLE 4 l. Knitted polyamidefabric; weight 132 g/m 2. Continuous fibrous fleece of a mixture of 30 percent of poly-2,6-pyridinoyl oxalamidrazone and 70 percent of cellulose having a zinc content of 11.5 percent by weight; weight 69 g/m*.

3. Crimped fleece of polyethylene terephthalate;

weight 150 g/m 4. Continuous fibrous fleece of a mixture of 40 percent of polyterephthaloyl oxalamidrazone and 60 percent of cellulose having a tin content of percent by weight; weight 286 g/m The weight of this composite sheet of four layers of insulating material is 637 glm the permeability to air is 349 1/100 cm min. and the thermal efficiency is 65.4 percent.

EXAMPLE 5 l. Knitted fabric of polyterephthaloyl oxalamidra zone having a tin content of percent by weight;

weight 418 'g/m.

2. Stitched fleece of a mixture of 40 percent of polyterephthaloyl oxalamidrazone and 60 percent of cellulose having a tin content of percent by weight; weight 94 g/m.

3. Knitted fabric of polyterephthaloyl oxalamidrazone having a tin content of 30 percent by weight; weight 418 g/m The weight of this composite sheet of three layers of insulating material is 930 g/m the permeability to air is 576 l/lOO cm'-" min. and the thermal efficiency is 52 percent.

The sheets or other fabricated articles of insulating material according to the invention are distinguished from those previously known not only by their excellent protective action against flames and high temperatures but also by the balanced relationship between their premeability to air and their capacity for heat retention, by virtue of the distinct textile character of the material which forms the essentially flame-resistant layers, i.e., the difficultly combustible and flameproof layers. As a result, these sheets of insulating material have excellent physiological properties for manufacture into garments of all kinds. The articles of insulating material according to the invention also have the advantage over known materials of this kind by being relatively light in weight and still providing an undiminished resistance to heat and flame even after they have been washed or cleaned many times. It will therefore be readily apparent that the insulating material according to the invention affords outstanding advantages in the manufacture of protective clothing and rescue suits of the type used for aviation and navigation, in firefighting and in industrial and for military applications.

Furthermore, the articles of insulating material according to the invention are not limited to clothing or protective garments but may be used wherever it is important to prevent the breaking out and spreading of fires. For example, composite sheets of these materials are suitable as lining materials for theaters, movie houses, storage rooms, warehouses and the like as well as passenger carbons and freight compartments in ships, motor vehicles and aircraft.

For protection against intensive heat of radiation, one of the outer surface layers of the composite sheet of insulating material is advantageously metallized, i.e., coated with a metallic film or surface layer in a conventional manner in which the metal is mechanically or physically bonded to the fibrous layer which is preferably a woven/knitted fabric. Such metallized surface layers, especially in combination with at least one flameresistant layer of the invention are especially effective in achieving a highly flexible flame-proof covering article.

In each of the foregoing examples, the metal is chemically bound with the polyacyloxalamidrazone fiber or the bicomponent fiber of this polymer with cellulose by immersing the textile fibers or filaments in an aqueous bath containing one of the following compounds in solution in the concentration shown:

Example Layer Solvent In addition to these useful metal compounds, many others can also be used, including merely by way of example: 3 CdSO 8H O (in 2n NH OH), Ba(Ol-l) Sr (OH SbCl (in dimethylformamide) and TaSO These metals in dissolved form, i.e., in aqueous solution, are very easily taken up in chemically combined form by the polyacyloxalamidrazone but probably at various random and indeterminable points along the molecular chain of the poiymer. Any minimum amount of metal can feasibly be incorporated in the polymer by the bath treatment, but it is of course important in providing a highly flame-resistant material to achieve a relatively high content of the metal in the polymer, e.g., about 15 percent weight or more.

In one sense, the present invention resides in the specific flame-resistant fibers of metalpolyacyloxalamidrazone alone or especially in admixture with the coprccipitated cellulosic polymer. However, it is the highly improved textile qualities of these fibers which permits them to be readily employed in multilayer flame-resistant and insulating sheets, webs or similar articles. The resulting improvement in the finished article itself represents a very unusual advance in this particular art in terms of both lightweight and washable materials of excellent flame resistance and insulation against high temperatures.

The invention is hereby claimed as follows:

1. A multilayer fibrous insulating article comprising at least one flame-resistant layer containing fibers composed of a polyacyloxalamidrazone in complex chemical combination with at least one metal selected from the group consisting of zinc, tin, cadmium, barium, strontium, calcium, antimony and tantalum.

2. An insulating article as claimed in claim 1 wherein said flame-resistant layer consists essentially of a fibrous material which is a mixture of (A) cellulose and (B) said polyacyloxalamidrazone in complex chemical combination with at least one of said metals.

3. An insulating article as claimed in claim 2 wherein the proportion of the polyacylamidrazone in said mixture is at least about 20 percent by weight.

4. An insulating article as claimed in claim 2 wherein the proportion of the polyacylamidrazone in said mixture is about 30 to 70 percent by weight, the proportion of cellulose being 70 to 30 percent by weight.

5. An insulating article as claimed in claim 2 wherein the proportion of the polyacylamidrazone in said mixture is about 40 to 50 percent by weight, the proportion of cellulose being 60 to 50 percent by weight.

6. An insulating article as claimed in claim 1 wherein the amount of metal in complex chemical combination is at least about 15 percent by weight with reference to the polyacyloxalamidrazone.

7. An insulating article as claimed in claim 6 wherein said metal is a member selected from the group consisting of zinc, tin and calcium.

8. An insulating article as claimed in claim 6 wherein the polyacyloxalamidrazone is polyterephthaloyl oxalamidrazone.

9. An insulating article as claimed in claim 7 wherein the polyacyloxalamidrazone is polyterephthaloyl oxalamidrazone.

10. An insulating article as claimed in claim 1 wherein the flame-resistant layer includes 50 to 100 percent by weight of said polyacyloxalamidrazone combined with said metal and the total weight of said layer is about 50 to 300 grams per square meter.

11. An insulating article as claimed in claim 10 wherein the total weight of all fibrous layers of the article is about 300 to l,000 grams per square meter.

12. An insulating article as claimed in claim 1 wherein at least one outer layer of fibrous insulating material is a woven or knitted fabric formed of yarn containing said polyacyloxalamidrazone combined with said metal.

13. An insulating article as claimed in claim 1 wherein at least one inner layer of fibrous insulating material is a voluminous fleece formed of fibers containing said polyacyloxalamidrazone combined with said metal.

14. An insulating article as claimed in claim 1 wherein an outer surface layer of the fibrous material is metallized.

15. An insulating article as claimed in claim 1 which contains in addition to said flame-resistant layer at least one heat-insulating lay'er composed of a fibrous polyester fleece.

16. An insulating article as claimed in claim 1 wherein the total weight of all fibrous layers in said arti- ,cle is about 300 to 1,000 grams per square meter.

17. An insulating article as claimed in claim 2 wherein said fibrous material of the flame-resistant layer is formed by spinning in common a mixture of fiber-forming cellulose and polyacyloxalamidrazo'ne as an aqueous alkaline solution thereof into an acid precipitation bath, withdrawing the precipitated filaments therefrom and reacting the filaments with an aqueous solution of at least one water-soluble compound of said metal.

18. An insulating article as claimed in claim 17 wherein said metal is selected from the group consisting of zinc, tin and calcium.

19. An insulating article as claimed in claim 17 wherein said fibrous material is composed of about 30 to percent by weight of said polyacyloxalamidrazone and 70 to 30 percent by weight of cellulose.

20. An insulating article as claimed in claim 19 wherein said fibrous material contains at least 15 percent by weight of said metal with reference to the polyacyloxalamidrazone.

21. An insulating article as claimed in claim 20 wherein said polyacyloxalamidrazone is polyterephthaloyl oxalamidrazone. 

2. An insulating article as claimed in claim 1 wherein said flame-resistant layer consists essentially of a fibrous material which is a mixture of (A) cellulose and (B) said polyacyloxalamidrazone in complex chemical combination with at least one of said metals.
 3. An insulating article as claimed in claim 2 wherein the proportion of the polyacylamidrazone in said mixture is at least about 20 percent by weight.
 4. An insulating article as claimed in claim 2 wherein the proportion of the polyacylamidrazone in said mixture is about 30 to 70 percent by weight, the proportion of cellulose being 70 to 30 percent by weight.
 5. An insulating article as claimed in claim 2 wherein the proportion of the polyacylamidrazone in said mixture is about 40 to 50 percent by weight, the proportion of cellulose being 60 to 50 percent by weight.
 6. An insulating article as claimed in claim 1 wherein the amount of metal in complex chemical combination is at least about 15 percent by weight with reference to the polyacyloxalamidrazone.
 7. An insulating article as claimed in claim 6 wherein said metal is a member selected from the group consisting of zinc, tin and calcium.
 8. An insulating article as claimed in claim 6 wherein the polyacyloxalamidrazone is polyterephthaloyl oxalamidrazone.
 9. An insulating article as claimed in claim 7 wherein the polyacyloxalamidrazone is polyterephthaloyl oxalamidrazone.
 10. An insulating article as claimed in claim 1 wherein the flame-resistant layer includes 50 to 100 percent by weight of said polyacyloxalamidrazone combined with said metal and the total weight of said layer is about 50 to 300 grams per square meter.
 11. An insulating article as claimed in claim 10 wherein the total weight of all fibrous layers of the article is about 300 to 1,000 grams per square meter.
 12. An insulating article as claimed in claim 1 wherein at least one outer layer of fibrous insulating material is a woven or knitted fabric formed of yarn containing said polyacyloxalamidrazone combined with said metal.
 13. An insulating article as claimed in claim 1 wherein at least one inner layer of fibrous insulating material is a voluminous fleece formed of fibers containing said polyacyloxalamidrazone combined with said metal.
 14. An insulating article as claimed in claim 1 wherein an outer surface layer of the fibrous material is metallized.
 15. An insulating article as claimed in claim 1 which contains in addition to said flame-resistant layer at least one heat-insulating layer composed of a fibrous polyester fleece.
 16. An insulating article as claimed in claim 1 wherein the total weight of all fibrous layers in said article is about 300 to 1,000 grams per squaRe meter.
 17. An insulating article as claimed in claim 2 wherein said fibrous material of the flame-resistant layer is formed by spinning in common a mixture of fiber-forming cellulose and polyacyloxalamidrazone as an aqueous alkaline solution thereof into an acid precipitation bath, withdrawing the precipitated filaments therefrom and reacting the filaments with an aqueous solution of at least one water-soluble compound of said metal.
 18. An insulating article as claimed in claim 17 wherein said metal is selected from the group consisting of zinc, tin and calcium.
 19. An insulating article as claimed in claim 17 wherein said fibrous material is composed of about 30 to 70 percent by weight of said polyacyloxalamidrazone and 70 to 30 percent by weight of cellulose.
 20. An insulating article as claimed in claim 19 wherein said fibrous material contains at least 15 percent by weight of said metal with reference to the polyacyloxalamidrazone.
 21. An insulating article as claimed in claim 20 wherein said polyacyloxalamidrazone is polyterephthaloyl oxalamidrazone. 